1. Field of the Invention
The present invention relates to a gas generator suitable for an air bag system carried on a vehicle and to an air bag apparatus.
2. Description of the Related Art
A gas generator for an air bag serves to supply into the air bag an inflation gas for protecting an occupant. A recent trend to cost down led to the simplification of the bag itself and the use of thin cloths. Therefore, if impurities are present in the generated gas, the bag cloth can be ruptured by the ejection of the gas from the gas generator. Therefore, the generated gas from the gas generator has to be clean.
In particular, when the gas generator is a pyrotechnic type gas generator in which the combustion gas is generated by burning a solid gas generating agent, combustion residues are generated. For this reason, a filter for filtering and cooling the combustion residues has been conventionally used in the pyrotechnic type gas generators.
In the pyrotechnic type gas generators, the housing is most often made from aluminum or the internal structure is simplified to reduce weight. For this reason, the pressure inside the housing sometimes rises at the same time as the gas generating agent starts to burn, and the housing is deformed by this pressure. As long as the housing strength is maintained, the deformation itself causes no problem. However, the deformation creates a gap between the filter and the housing wall surface that is in contact with the filter, and there is a risk that a short path phenomenon will occur in which a combustion gas that has not yet been sufficiently cooled and purified is discharged into the air bag.
US-A No. 2003/0047925 is a prior art relating to the present invention. In this gas generator, a single space is formed inside the gas generator by a combination of a base 16 and a cap 14, and a gas generating agent 23, a filter, 28, and an igniter 18 are disposed therein.
However, in the above-described conventional gas generator, the respective parts of the outer peripheral surface on the upper and lower end sides of the filter 28 abut against the inner peripheral surface of the housing, making it difficult for the gas to pass in those portions and decreasing the efficiency of cooling and purification. As a result, an adverse effect is produced on the bag cloth.
Other prior arts are JP-A No. 9-226509, JP-A No. 11-5508 (corresponding to U.S. Pat. No. 5,951,040), JP-A No. 2002-370607 and U.S. Pat. No. 6,527,297.
JP-A No. 9-226509 discloses a gas generator for an air bag having a central ignition chamber in which ignition devices are arranged and a combustion chamber in which a gas generating agent and filter member are arranged.
JP-A No. 11-5508 discloses an air bag inflator including a housing and an inflation fluid source in the housing actuatable to provide a pressurized inflation fluid.
JP-A No. 2002-370607 discloses a single cylinder type gas generator including, in a housing, a filter material, a gas generating agent in a combustion chamber defined in the filter material, and a charge cylinder unit provided with a flame jet nozzle and including ignition means.
U.S. Pat. No. 6,527,297 discloses inflator device assemblies in which an igniter composition to ignite a gas generant material is provided on a selected surface, such as on a damper pad, within the inflator device.